JPH07270560A - Fast breeder reactor - Google Patents

Abstract

PURPOSE:To suppress thermal stress at the joint of a reactor vessel and an upper end plate by providing a thermal insulation member on the outside of the upper cover so that an equal temperature condition is realized for the reactor vessel and the upper cover thereof. CONSTITUTION:An upper end plate 17 is not provided with any thermal insulation member or cooling layer inside but a thermal insulation member 9 is provided outside. Consequently, the upper end plate 17 follows up the temperature of a reactor vessel 1 easily through radiation from an internal liquid metal 3 and thermal conduction from the vessel 1 touching the liquid metal 3. Since the temperature distribution is not developed significantly in the axial direction, thermal stress can be suppressed at the joint of the vessel 1 and the upper end plate 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast breeder reactor, and in particular, uses a fixed upper lid without using a rotary plug, and this upper lid is formed by an upper mirror to refuel a control rod drive mechanism. It relates to a fast breeder reactor that can be pulled up at times.

[0002]

2. Description of the Related Art A fast breeder reactor uses a mixed oxide fuel of uranium and plutonium to fission Pu239 and generate excess fast neutrons from surrounding U238.
Since it produces more plutonium than it absorbs and burns, it holds great promise as a future energy source.

FIG. 10 shows a schematic structure of a conventional fast breeder reactor. As shown in FIG. 10, inside a bottomed cylindrical reactor vessel 1, a reactor core 2 for generating thermal energy by a nuclear reaction is provided. In addition, inside the reactor vessel 1, liquid metal (usually liquid sodium) is used as a primary coolant.
A plurality of coolant inlet pipes 4 for guiding the coolant 3 to the core 2, and a plurality of coolant outlet pipes 5 for guiding the coolant from the core 2 to an intermediate heat exchanger (not shown) installed outside the reactor vessel 1 respectively. It is arranged. All of the plurality of coolant inlet pipes 4 and the plurality of coolant outlet pipes 5 are arranged in the reactor vessel 1 at equal intervals in the circumferential direction.

A core inlet plenum portion 6 is provided below the core 2, and the core 2 and the core inlet plenum portion 6 are supported by a core support 7 provided at the bottom of the reactor vessel 1. A core upper mechanism 8 is installed above the core 2.

A safety container (guard vessel) 14 having a bottomed cylindrical shape is provided on the outside of the reactor vessel 1 in case of a coolant leakage accident, and a seismic support 13 is installed through the safety vessel 14. Has been done. The fast breeder reactor thus configured is supported by the cavity wall 16 of the reactor building via the support member 15 provided on the outer periphery of the upper portion.

Further, the upper opening of the reactor vessel 1 is closed by a roof deck 12 constituting an upper lid, and a cooling layer 18 is installed on the lower surface of the roof deck 12, and a cooling gas is circulated through the cooling layer 18. By doing so, heating of the roof deck 12 is prevented. A liquid metal 3 is contained in the reactor vessel 1 as a primary coolant, and an inert gas such as argon gas is filled between the liquid surface of the liquid metal 3 and the roof deck 12 to cover gas. A space 19 is formed.

Further, a control rod drive mechanism is installed in the upper core mechanism 8, and this control rod drive mechanism controls the output by moving the control rod in and out of the core during the operation of the reactor. At the time of refueling, the rotary plug 20 is rotated to move the core upper part mechanism 8 from the upper part of the core 2, and the fuel in the core 2 is replaced by the fuel exchanger.

As described above, in the conventional reactor upper structure, the core upper mechanism 8 is retracted from the upper portion of the core 2 for refueling, and the refueling machine is moved to each fuel position of the core 2. Twenty.

Next, the operation of the conventional fast breeder reactor will be described.

First, the liquid metal 3 as the primary coolant is guided to the coolant inlet pipe 4 and flows into the core inlet plenum portion 6. While entering from the core inlet plenum portion 6 and passing upward through the core 2, the liquid metal 3 is heated to a high temperature by receiving thermal energy due to a nuclear reaction, and is guided to the coolant outlet pipe 5 so as to be guided to the reactor outlet pipe 1. It flows into an intermediate heat exchanger (not shown) installed outside. The liquid metal as the secondary coolant heated by the intermediate heat exchanger heats the steam for driving the turbine. And the operation control of the reactor is
This is performed by inserting or pulling out the control rod of the core upper part mechanism 8 installed on the core 2 into the core 2.

[0011]

However, in the conventional fast breeder reactor configured as described above, the rotating plug 20 which is equipped with the fuel exchanger and the upper core mechanism 8 and rotates.
Including radiation shields and heat insulation structures, the weight reaches hundreds of tons. The upper part of the reactor has an extremely complicated structure due to a large number of equipments (gears, driving devices, bearings, rotating part airtight device, rotating part cable processing device, etc.) required for this rotary drive. As a result, design, manufacturing, installation, assembly,
A great deal of labor is required for testing and inspection.

As described above, since the conventional fast breeder reactor uses the rotating plug 20 for refueling, it occupies a large space in the upper part of the reactor, resulting in a problem that the reactor vessel becomes large. is there.

Further, in the fast breeder reactor, in order to absorb the increase in volume due to the thermal expansion of sodium as a coolant, a free liquid level is set in the loop of primary sodium and the volume expansion is absorbed in the remaining gas space. It is necessary to. The lower side of the liquid surface of the reactor vessel 1 is in contact with sodium and has good heat transfer with sodium, so that the temperature of the vessel follows the temperature of sodium. On the other hand, the upper side of the liquid surface is covered with a cover gas space 19 filled with an inert gas such as argon gas. The temperature of this cover gas space 19 follows the temperature change of sodium.

Since the structure of the roof deck 12 is a welded assembly structure, it is necessary to limit the temperature to a relatively low temperature of about 100 ° C. or less. This is for avoiding large deformation due to temperature distribution, for being in direct contact with the cavity wall 16 made of concrete, and for ensuring the soundness of concrete.

Therefore, the cooling layer 18 is installed on the lower surface of the roof deck 12 so that the roof deck 12 does not follow the temperature of the cover gas space 19. With such a structure, a temperature distribution in the vertical axis direction of the reactor vessel 1 may occur, and a large thermal stress may occur at the joint between the reactor vessel 1 and the roof deck 12. Therefore, the vicinity of the root portion of the roof deck 12 of the reactor vessel 1 is protected by the heat insulating material 21,
The thermal stress is reduced by optimizing the temperature distribution.

That is, while the rotary plug 20 is cooled, the temperature near the liquid surface of the liquid metal 3 of the reactor vessel 1 is high, and as a result, the axial temperature difference of the reactor vessel 1 in this region is large, and Since the directional length is short, the temperature gradient becomes large. Since this causes an increase in thermal stress, from the viewpoint of heat resistance, it is necessary to provide a reactor wall heat protection structure such as the heat insulating material 21 at the liquid level part of the liquid metal 3 of the reactor vessel 1. It was

However, as in the case of a reactor having a diameter of about 10 m and a plate thickness of about 50 mm shown in FIG. 10, thermal stress near the root of the roof deck 12 is sensitive to the performance of the heat insulating material 21 as shown in FIG. Therefore, the degree of freedom in design was reduced.

Further, in the conventional fast breeder reactor, since the reactor vessel 1 is supported by the cavity wall 16 of the reactor building through the support member 15 provided on the outer periphery of the upper portion, the load transfer of the core weight is carried out. The path is composed of the body of the reactor vessel 1 and the lower mirror, and the vibration characteristics of the reactor vessel 1 easily affect the core 2. Therefore, it was necessary to install a seismic isolation structure for the reactor building to reduce the earthquake input or seismic support to reduce the seismic response.

Further, in the conventional fast breeder reactor, in order to detect the closed state of the fuel assembly of the core 2, 200 to 300
Thermocouples are arranged at the outlets of the fuel assemblies of the book, and the temperature rise is monitored for each fuel assembly. Then, in order to guide the thermocouple to the outlet of each fuel assembly, it is necessary to install a large number of thermocouple guide tubes in the upper part of the reactor, which causes a problem that the structure of the core upper part mechanism becomes complicated.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a fast breeder reactor having a simplified reactor upper structure by eliminating the rotary plug. .

Another object of the present invention is to:
It is an object of the present invention to provide a fast breeder reactor capable of reducing the thermal stress of the reactor wall of the reactor vessel and improving the seismic resistance of the reactor core.

[0022]

In order to solve the above-mentioned problems, the first aspect of the present invention provides a reactor vessel containing a core and a coolant, an upper lid of the reactor vessel, and An upper mirror that is in an isothermal state with the reactor vessel, a control rod drive mechanism that drives a control rod that is installed in the reactor vessel from above the upper lid and controls the nuclear reaction, and is placed above the core during refueling. It is characterized by including a fuel exchanger capable of exchanging fuel at an arbitrary position and an elevating device for raising the control rod drive mechanism to a movable range of the fuel exchanger.

According to a second aspect of the present invention, in the fast breeder reactor according to the first aspect, the control rod drive mechanism has an upper guide tube for guiding a drive shaft pulled up by the elevating device removed.

According to a third aspect of the present invention, in the fast breeder reactor according to the first aspect, there is provided a core upper part mechanism for supporting a fuel assembly outlet temperature instrumentation for measuring an outlet temperature of a fuel assembly forming the core, This core upper part mechanism is characterized in that it is lifted up to a movable range of the refueling machine together with the control rod drive mechanism at the time of refueling.

A fourth aspect of the present invention is the fast breeder reactor according to the first aspect, wherein a heat insulating material is provided outside the upper mirror.

According to a fifth aspect of the present invention, in the fast breeder reactor according to the first aspect, a support for supporting the core and the reactor vessel from below is provided.
Alternatively, in the fast breeder reactor according to the third aspect, a plurality of ultrasonic sensors for detecting the temperature are installed around the upper portion of the fuel assembly of the core.

[0027]

According to the first aspect of the present invention, since the upper mirror forming the upper lid of the reactor vessel is in an isothermal state with the reactor vessel, a large temperature difference does not occur between the reactor vessel and the upper mirror. Therefore, the thermal stress at the joint between the reactor vessel and the upper mirror can be easily reduced.

Further, according to the first aspect of the present invention, when the fuel is exchanged, the control rod drive mechanism is lifted up to the movable range of the fuel exchanger by the elevating device so that the fuel exchanger can exchange the fuel at any position. Therefore, the conventional rotary plug is not required, and the reactor superstructure can be simplified.

In the second aspect of the present invention, in the control rod drive mechanism according to the first aspect, since the upper guide tube for guiding the drive shaft pulled up by the lifting device is removed, the control rod drive mechanism can be pulled up at the time of refueling. It is simplified.

According to a third aspect of the present invention, there is provided an upper core mechanism for supporting the fuel assembly outlet temperature instrumentation for measuring the outlet temperature of the fuel assembly constituting the core according to the first aspect. When the fuel is exchanged, the fuel exchange can be exchanged with fuel at any position by raising the control rod drive mechanism to the movable range of the fuel exchange. Therefore, the conventional rotary plug is not required, and the reactor superstructure can be simplified.

According to a fourth aspect of the present invention, by providing a heat insulating material on the outside of the upper mirror according to the first aspect, the upper mirror is radiated from the coolant inside and the reactor vessel in contact with the coolant. The temperature of the reactor vessel can be easily followed by the heat conduction of. For this reason, without providing a cooling layer, a large temperature distribution does not act in the axial direction, and the thermal stress at the joint between the reactor vessel and the upper mirror can be suppressed low.

According to a fifth aspect of the present invention, by providing a support for supporting the reactor vessel according to the first aspect from below,
There is no need for the top lid to come into contact with concrete, and there is no need to cool the top lid. Therefore, the same operation as that of claim 4 is performed.

Further, in the present invention, since the core is supported from below by the support, the seismic load input position moves downward, and the reactor vessel is excluded from the load transfer path, so that the reactor building is removed from the core. Since the load transmission path up to is shortened and the seismic load of the reactor building is amplified and the multiplication factor transmitted to the core is reduced, the seismic response at the core position is mitigated.

According to a sixth aspect of the present invention, a plurality of ultrasonic sensors for detecting the temperature are installed around the upper portion of the fuel assembly of the core according to the first or third aspect, so that the outlet temperature of the fuel assembly is ultrasonically detected. Can be detected as a change in sound velocity and monitored by telemetry.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view showing an embodiment of the fast breeder reactor according to the present invention. It should be noted that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals as those in FIG. As shown in FIG. 1, a reactor core 1 for generating thermal energy by a nuclear reaction is provided inside a bottomed cylindrical reactor vessel 1. In addition, inside the reactor vessel 1,
Plural coolant inlet pipes 4 for guiding liquid metal (usually liquid sodium) 3 to the core 2 as a primary coolant, an intermediate heat exchanger (not shown) installed outside the reactor vessel 1 from the core 2
A plurality of coolant outlet pipes 5 that guide the coolant to are respectively provided. All of the plurality of coolant inlet pipes 4 and the plurality of coolant outlet pipes 5 are arranged in the reactor vessel 1 at equal intervals in the circumferential direction.

A core inlet plenum portion 6 is provided below the core 2, and the core 2 and the core inlet plenum portion 6 are supported by a core support 7 provided at the bottom of the reactor vessel 1. An upper core mechanism 8 that supports a fuel assembly outlet temperature instrumentation that measures an outlet temperature of a fuel assembly forming the core 2 is installed above the core 2.

The upper opening of the reactor vessel 1 is closed by an upper mirror 17 which forms an upper lid 10 and is in an isothermal state with the reactor vessel 1. Liquid metal 3 is housed in the reactor vessel 1 as a primary coolant, and an inert gas such as argon gas is filled between the liquid surface of the liquid metal 3 and the upper mirror 17, and the cover gas space 19 Are formed. A heat insulating layer and a cooling layer are not provided inside the upper mirror 17, the inner surface of the upper mirror 17 is in contact with the cover gas space 19, and the heat insulating material 9 having excellent heat insulating performance is arranged on the outer surface thereof. The temperature near the liquid surface of the metal 3 is prevented from changing rapidly.

A safety container 14 having a cylindrical shape with a bottom is provided outside the reactor vessel 1 in case of a coolant leakage accident. The reactor vessel 1 and the core 2 are supported from below by a support skirt 23 as a support placed on the base mat 22 of the reactor building.

Next, the overall operation of this embodiment will be described.

The liquid metal 3, which is the primary coolant, is sent to an intermediate heat exchanger (not shown) installed outside the reactor vessel 1 as in the conventional case, and heated by this intermediate heat exchanger. The liquid metal as the secondary coolant heats the steam for driving the turbine.

When the reactor is shifted from the low temperature state to the rated output operating state through the high temperature standby state, the temperature near the liquid surface of the liquid metal 3 in the reactor vessel 1 rises, but the reactor vessel 1 The temperature of the upper mirror 17 also rises from the liquid surface of the liquid metal 3 through the cover gas space 19 by radiant heat transfer and convective heat transfer, and the outside of the upper mirror 17 is insulated by the heat insulating material 9. The temperature difference along the reactor vessel 1 above the vicinity of the liquid surface of the reactor vessel 1 does not increase. Further, even in the stop operation of shifting from the high temperature state to the low temperature state contrary to the increase in the output of the nuclear reactor, the upper mirror 17 of the reactor vessel 1 is also affected by the temperature change in the vicinity of the liquid surface of the liquid metal 3 as at the time of startup. It becomes possible to follow.

That is, in the upper mirror 17, since the heat insulating material and the cooling layer are not installed inside and the heat insulating material 9 is installed outside, radiation from the liquid metal 3 inside and contact with the liquid metal 3 Due to the heat conduction from the operating reactor vessel 1,
It easily follows the same temperature as the reactor vessel 1. Therefore, the thermal stress at the joint between the reactor vessel 1 and the upper mirror 17 can be suppressed low without a large temperature distribution acting in the axial direction.

On the other hand, since the core 2 is directly supported by the base mat 22 of the reactor building via the support skirt 23, the input seismic load is reduced. In addition, the cylindrical body of the reactor vessel 1 is excluded from the load transfer path, and the load transfer distance from the core 2 to the reactor building is shortened, so that the seismic load of the reactor building is amplified and Since the transmitted multiplication factor is reduced, the seismic response at the core 2 position is mitigated.

Here, since the cylindrical body of the reactor vessel 1 is excluded from the load transfer path, the seismic load has a mitigating effect not only on horizontal earthquakes but also on vertical motion during vertical earthquakes. As a result, it is effective in mitigating the seismic response at the core 2 position even when a horizontal earthquake and a vertical earthquake are superposed.

As described above, according to the present embodiment, the temperature gradient near the liquid surface of the reactor vessel 1 where the severest thermal stress is generated in the conventional reactor structure becomes gentle, and the thermal stress can be reduced. Therefore, the furnace wall cooling device and the furnace wall heat protection structure, which are necessary for this, are not required. In addition, since the response load during an earthquake at the core 2 position is reduced, the reactor building seismic isolation structure for reducing the load applied to the core 2 and the seismic support for reducing the seismic response are not required. The diameter of the reactor vessel 1 can be reduced without disposing an extra device around the reactor vessel 1 in the reactor.

Next, from the upper side of the upper lid 10, the reactor vessel 1
The control rod drive mechanism 25 that drives the control rod that is installed inside and controls the nuclear reaction will be described with reference to FIG. The control rod drive mechanism 25 is lifted up to a movable range of a refueling machine, which will be described later, by the lifting device 24 during refueling.
The control rod drive mechanism 25, as shown in FIG.
6 and a motor 27 is provided in the upper part of the housing 26.
Is installed, and by driving this motor 27, the screw shafts 28, 28 rotate via a gear (not shown) or the like. A ball nut 29 is screwed onto the screw shafts 28, 28, and an electromagnet 30 is fixed to the ball nut 29.

Further, a latch mechanism 31 is attached to the electromagnet 30 so as to be able to come into contact with and separate from the electromagnet 30, and a drive shaft 32 is attached to a lower portion of the latch mechanism 31.
A cover gas seal 33 is provided at the insertion portion of the. An upper guide tube for guiding the movement of the drive shaft 32 is removed, while a short guide tube 34 is provided in the core upper mechanism 8. A control rod 35 disposed in a lower guide tube 36 is attached to the lower end of the drive shaft 32 so that the control rod 35 can come into contact with and separate from the drive rod 32.

A dash ram 37 is provided on the drive shaft 32, and a dash pot 3 for supporting the dash ram 37.
8 is fixed to the inner surface of the guide tube 34. At the time of an emergency stop of the nuclear reactor, the drive shaft 32 and the control rod 35 are integrally dropped by demagnetizing the electromagnet 30, and the shock at this time is absorbed by the dash ram 37 and the dash pot 38.

Further, at the time of refueling, the screw shafts 28, 28 are rotated by driving the motor 27 after separating the lower end of the drive shaft 32 from the control rod 35 as shown in FIG. By the rotation of the screw shafts 28, 28, the ball nut 29 restrained in the rotation direction moves upward, the drive shaft 32 is pulled up via the electromagnet 30 and the latch mechanism 31, and the space S necessary for refueling is secured. be able to.

Therefore, by removing the upper guide tube for guiding the drive shaft 32, there is no obstacle to pulling up the control rod drive mechanism 25 at the time of fuel replacement, and the operation is simplified. Further, the control rod drive mechanism 25 is light and simple, and the fuel can be easily exchanged.

FIG. 4 is a vertical cross-sectional view showing a state of refueling the fast breeder reactor according to this embodiment. The control rod drive mechanism 25 at the time of refueling is pulled up as described above, while the upper core mechanism 8 is pulled up by the elevating drive device 40 via the columns 41. After that, the refueling machine 42 is replaced by the upper lid 10.
The variable arm 43, which is mounted and supported by the robot, is extended to a predetermined position, and a predetermined fuel element in the core 2 is pulled out and stored in the gripper device 44, and then the entire fuel exchanger 42 is moved to the fuel relay tank 45. Store elements. In this way, all the fuel elements in the core 2 can be transferred to the fuel relay tank 45.

Further, in order to take out the fuel from the fuel relay tank 45 to the outside of the reactor, a gripper (not shown) is inserted into the reactor from the chute 47 of the fuel loading / unloading unit 46 installed through the upper mirror 17 of the reactor vessel 1. Then, the fuel element in the fuel relay tank 45 is gripped and pulled up.

Therefore, at the time of refueling, the control rod drive mechanism 25 is lifted up to the movable range of the refueling machine 42 by the elevating device 24, so that the refueling machine 42 can replace the fuel at any position. Therefore,
There is no need for a rotating plug that rotates by mounting a refueling machine or control rod drive mechanism as in the past, and a large number of equipment required for rotation (gear, drive device, bearing, rotating part airtight device, rotating part cable processing device). Is unnecessary. As a result, the structure is greatly simplified, and the design, manufacturing, installation, assembly, and test equipment is simplified. In addition, the equipment arranged in the upper part of the reactor becomes smaller, and as a result, the diameter of the reactor vessel can be reduced.

FIG. 5 is a plan view showing the upper portion of the core in which ultrasonic sensors are installed in the fast breeder reactor according to this embodiment.
As shown in FIG. 5, the core fuel assembly 50, the control rods 35, etc. are arranged in the core 2, and six columns 41 are installed in the upper part of the core 2, and the cores are provided between these columns 41. Beams 51 are laid across the top of the fuel assembly 50 by about 50 to 100 mm. These beams 5
1, a plurality of ultrasonic sensors 52 (52a to 52d) are arranged so as to surround the core fuel assembly 50,
They are arranged so that they can transmit and receive ultrasonic waves to each other.

FIG. 6 shows the vertical structure of the core upper part mechanism. As shown in FIG. 6, the ultrasonic sensor 52 is guided to a predetermined position by a guide tube 53 passing through the support column 41. 53 is formed in a rectangular shape as shown in FIG. 7, and the ultrasonic sensor 52 connected to a mineral insulated (MI) cable 54 is inserted therein.

Next, the operation of the ultrasonic sensor 5 in this embodiment will be described.

The ultrasonic sensor 52 can scan the outlet temperature of the core fuel assembly 50 by the guide tube 53 passing through the support column 41, and is guided to a position surrounding the core fuel assembly 50. Further, by using the guide tube 53 formed in a rectangular shape, the ultrasonic sensor 52 can be aligned with the facing ultrasonic sensor.

By the way, the temperature T (° C.) of sodium which is a liquid metal and the sound velocity C (m / sec) of ultrasonic waves have the following relationship.

[0060]

## EQU1 ## C = 2577.25-0.524 × T

Therefore, as the temperature of sodium increases, the speed of sound decreases. Here, it is assumed that the outlet temperature of the core fuel assembly 50 has risen. When a pulse wave is transmitted from the ultrasonic sensor 52a and received by the ultrasonic sensor 52b,
As the fuel assembly outlet temperature rises, the pulse interval between transmission and reception increases. In addition, when a pulse wave is transmitted from the ultrasonic sensor 52c and received by the ultrasonic sensor 52d, the pulse interval between transmission and reception increases as the fuel assembly outlet temperature rises. That is, the temperature of the core fuel assembly 50 is increased by transmitting and receiving ultrasonic pulses in two or more directions.
The position of can be identified, and the temperature can be measured from the increased value of the pulse interval.

Since the ultrasonic sensor 52 is arranged as described above, it is possible to replace the ultrasonic sensor 52 when there is a problem, and the guide tubes 53 are only the number corresponding to the ultrasonic sensor 52. The number can be significantly reduced. Further, the outlet temperature of the core fuel assemblies 50 can be detected as a change in sound velocity using ultrasonic waves, and the outlet temperatures of all the core fuel assemblies 50 can be monitored by remote measurement.

8 and 9 show another arrangement of the ultrasonic sensors in this embodiment, and FIG. 8 shows the vertical structure of the core upper part mechanism. As shown in FIG. 8, beams 51 are bridged between the columns 41, and the columns 41 and 51 are provided with guide rails 55 extending from the columns 41 to the columns 51. This guide rail 55
A plurality of holders 56 are connected and housed therein, and an ultrasonic sensor 52 is provided in these holders 56.

Then, as shown in FIG. 9, a guide roller 57 is attached to the connecting portion of the plurality of holders 56,
A plurality of holders 5 connected by this guide roller 57
6 can be guided along the guide rail 55.

Next, the operation of the ultrasonic sensor 52 arranged as described above will be described.

The ultrasonic sensor 52 is composed of the column 41 to the beam 51.
The exit temperature of the core fuel assembly 50 can be scanned by the guide rail 55 passing through the core fuel assembly 50.
Is led to the position surrounding the. Further, since the guide roller 57 is rotated along the two guide rails 55 to move the holder 56, the orientation of the holder 56 is regulated and the ultrasonic sensor 52 can be aligned with the opposing ultrasonic sensor. it can.

With the above structure, the ultrasonic sensor 52 can be replaced when it is defective, and the ultrasonic sensor 52 is guided by the guide rail 55 passing from the column 41 to the beam 51. No guide tube is required, the furnace upper structure can be simplified, and the reliability can be improved.

[0068]

As described above, according to the first aspect of the present invention.
According to this, since the upper mirror forming the upper lid of the reactor vessel is in an isothermal state with the reactor vessel, a large temperature difference does not occur between the reactor vessel and the upper mirror. Therefore, the thermal stress at the joint between the reactor vessel and the upper mirror can be easily reduced, which contributes to efficient operation of the reactor.

Further, according to the first aspect, when the fuel is exchanged, the control rod drive mechanism is lifted up to the movable range of the fuel exchanger by the elevating device so that the fuel exchanger can exchange the fuel at any position. Therefore, unlike the conventional case, a rotating plug that rotates by mounting a fuel exchanger or a control rod drive mechanism is unnecessary, and the reactor superstructure can be simplified.

According to a second aspect of the present invention, the control rod drive mechanism according to the first aspect is such that the upper guide tube for guiding the drive shaft pulled up by the lifting device is removed, so that the control rod drive mechanism is pulled up at the time of refueling. It is possible to simplify the operation and reduce the weight of the control rod drive mechanism. .

According to claim 3, there is provided a core upper part mechanism for supporting the fuel assembly outlet temperature instrumentation for measuring the outlet temperature of the fuel assembly constituting the core according to claim 1, and this core upper part mechanism. Is pulled up to the movable range of the refueling machine together with the control rod drive mechanism during refueling,
The refueling machine can exchange fuel at any position. Therefore, there is no need for the conventional rotary plug,
The reactor superstructure can be simplified.

According to a fourth aspect of the present invention, by providing a heat insulating material on the outer side of the upper mirror according to the first aspect, the upper mirror is in contact with the radiation from the coolant inside and the liquid in contact with the coolant. It easily follows the same temperature as the reactor vessel by heat conduction from the. For this reason, without providing a cooling layer, a large temperature distribution does not act in the axial direction, and the thermal stress at the joint between the reactor vessel and the upper mirror can be suppressed low.

According to the fifth aspect, by providing the support for supporting the reactor vessel according to the first aspect from below, it is not necessary for the upper lid to come into contact with concrete, and it is not necessary to cool the upper lid. Therefore, the same effect as the fourth aspect can be obtained.

According to the fifth aspect, since the core is supported from below by the support body, the seismic load input position moves downward, and the reactor vessel is excluded from the load transfer path so that the reactor is removed from the core. The load transmission path to the building is shortened, the seismic load of the reactor building is amplified, and the multiplication factor transmitted to the core is reduced, so that the seismic response at the core position is mitigated. As a result, the reactor building seismic isolation structure to reduce the load applied to the core and seismic support to reduce the seismic response are no longer required, and the reactor can be installed without extra equipment around the reactor vessel. It is possible to reduce the diameter of the furnace vessel.

According to claim 6, a plurality of ultrasonic sensors for detecting the temperature are installed around the upper portion of the fuel assembly of the core according to claim 1 or 3, so that the outlet temperature of the fuel assembly can be kept above the upper limit. Detects as a change in sound velocity using sound waves,
Monitoring can be done by telemetry.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a fast breeder reactor according to the present invention.

FIG. 2 is a configuration diagram showing a control rod drive mechanism in FIG.

FIG. 3 is a configuration diagram showing a state of the control rod drive mechanism in FIG. 1 during fuel replacement.

FIG. 4 is a vertical cross-sectional view showing a state of refueling the fast breeder reactor in FIG.

5 is a plan view showing an upper portion of a core provided with an ultrasonic sensor in the fast breeder reactor in FIG.

FIG. 6 is a schematic view showing an arrangement mode of the ultrasonic sensor in FIG. 5 on a core upper part mechanism.

FIG. 7 is an enlarged view showing an arrangement mode of the ultrasonic sensors in FIG.

FIG. 8 is a schematic view showing another arrangement mode of ultrasonic sensors in the core upper part mechanism.

9 is an enlarged view showing the ultrasonic sensor of FIG.

FIG. 10 is a vertical sectional view showing a conventional fast breeder reactor.

FIG. 11 is a diagram showing an example of calculation of thermal stress between the roof deck and the reactor vessel using the performance of the heat insulating material as a parameter in the conventional fast breeder reactor.

[Explanation of symbols]

 1 Reactor Vessel 2 Core 3 Liquid Metal 8 Core Upper Mechanism 9 Heat Insulating Material 10 Upper Lid 17 Upper Mirror 19 Cover Gas Space 22 Base Mat 23 Support Skirt (Support) 24 Elevator 25 Control Rod Drive Mechanism 32 Drive Shaft 35 Control Rod 40 Elevating / Driving Device 41 Support 42 Fuel Exchanger 46 Fuel Entry / Exit 47 Chute 50 Core Fuel Assembly 51 Beam 52 Ultrasonic Sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Araki 8 Shinsitata-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company inside Toshiba Yokohama Works (72) Kenichi Kubota 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Toshiba Corporation Yokohama Works (72) Inventor Koji Matsumoto 2-4 shares in Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Office (72) Inventor Takao Sato 4 shares 2 in Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Inside the Keihin Office (72) Inventor Yasuhiro Sakai 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Toshiba Keihin Office (72) Inventor Ryuji Ishitori 1 Komukai-Toshiba-cho, Kawasaki-shi, Kanagawa Stock Company Toshiba Research & Development Center (72) Inventor Nobuyuki Tanaka No. 1 Komukai Toshiba Town, Kawasaki City, Kanagawa Prefecture (72) Inventor Hiroshi Hirayama 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Ltd. Toshiba Corporation Yokohama office (72) Inventor Tokuyuki Takeshima 8-shin-Sugita-cho, Isogo-ku, Yokohama, Kanagawa In the office

Claims (6)

[Claims] 1. A reactor vessel containing a core and a coolant, an upper mirror forming an upper lid of the reactor vessel and being in an isothermal state with the reactor vessel, and a reactor vessel from above the upper lid. A control rod drive mechanism that is installed in the control rod for controlling a nuclear reaction, a fuel exchanger that is arranged above the core during fuel exchange and can exchange fuel at any position, and the control rod drive mechanism A fast breeder reactor, comprising: an elevating device that raises a switch to a movable range. 2. The fast breeder reactor according to claim 1, wherein the control rod drive mechanism has an upper guide tube for guiding a drive shaft pulled up by the lifting device removed. 3. The fast breeder reactor according to claim 1,
It has a core upper part mechanism supporting the fuel assembly outlet temperature instrumentation for measuring the outlet temperature of the fuel assembly that constitutes the core,
The fast breeder reactor is characterized in that the core upper part mechanism is lifted up to a movable range of the refueling machine together with the control rod driving mechanism at the time of refueling. 4. The fast breeder reactor according to claim 1, further comprising a heat insulating material provided outside the upper mirror. 5. The fast breeder reactor according to claim 1, further comprising a support for supporting the core and the reactor vessel from below. 6. The fast breeder reactor according to claim 1 or 3, wherein a plurality of ultrasonic sensors for detecting the temperature are installed around the upper portion of the fuel assembly of the core.